The present invention relates to the bending, levelling and straightening of workpieces by causing in the plastic deformation changes, and more particularly the invention relates to the bending, levelling and straightening of workpieces having combined plastic and elastic properties, under utilization of impacting elements which indent the material to be deformed for purposes of displacing and moving material so as to obtain changes in shape under utilization of acceleration and force application to the impacting or indent elements which provide for the deformation.
The deformation of workpieces made of material which are both, elastic as well as plastic, concerning any deformation, are known in a variety of ways and they are known as shot peen forming. This particular method of deforming is used e.g. for shaping the skin elements for the fuselage of an airplane or for wings of aircraft or for certain cell structures in space vehicles. In this case then one uses impact bodies (shot) in the form of steel balls or balls of any other material but of comparable hardness, or peening elements which are not balls but having other configurations. Forming and deforming of platelike or sheetlike workpieces obtains as a stream of shot moves towards the workpiece and performing local, peeninglike indentations. This working is carried out particularly on panels being constructed as integral components and to be used within certain assemblies; the integration involves particularly stiffening ribs on one side of the panel. Here one uses the indents (peening) bodies to impinge against the workpiece such that the peening bodies indent the surface of the workpiece. This procedure entails compacting of the material i.e. increasing its density, as well as material displacement which of course will result in an overall deformation if only one side of the object is affected.
The impact onto the workpiece to be deformed may e.g. involve free fall of the indenting and peening bodies and elements, from a particular height, and the indenting will depend also on the dimensions of the impact bodies or peening elements. The distribution of peening elements may provide a uniform or a nonuniform areal distribution as far as impact and indenting density is concerned. In a known form of practicing this method, small impact and peening bodies are accelerated in a suitable fashion e.g. by means of air or liquid or the shot is physically impelled through slings or the like. Other devices are known by means of which impact and indent bodies are individually accelerated through guide elements. Devices are also known for shaping and orienting sheet parts under utilization of indenting bodies arranged in a holder which penetrating bodies are rigid and oriented in relation to the plane.
The shot peening method using indenting bodies in forms of streams and/or fronts or shot and regardless of whether acceleration is used through gravity, gas or any other way, has as an inevitable side effect a significant scattering of the impacting peening bodies as the impinge on the workpiece. The scattering results from physical interaction and bouncing between bodies as they move towards the part but primarily of course through bounce back and reflection, back into the oncoming balls and shot. This reflection results on the average, in a significant scattering of the oncoming shot. Also a certain lack in homogeneity e.g. due to turbulence or the like provides for a difference in acceleration and therefore constitutes another scattering effect. Consequently these scatter effects produce certain tolerance zones including e.g. an imprecision in the boundary of the portion being deformed. Also, for statistical reasons random accumulations in excess of the normal impact and therefore excessive material displacement and irregular tension distribution seems unavoidable. Nonuniform material displacement is also the result of the fact that the impact bodies will impinge on the workpiece surface as straight on i.e. at right angles only in the average. In most instances there will be a lateral component.